First-filial-generation (F1) hybrids of genetically stable wild species are generally population with high genetic and morphological uniformity. Many interspecific cross combinations even within the same genus fail to produce hybrids, and therefore the cross compatibility can be determined only by actually practicing the cross. Ovule or embryo culture is in practical use as a method for breaking cross incompatibility barriers. However, only some interspecific combinations can provide hybrids even by this technique, and unless the culture is actually performed, whether hybrids can successfully be produced can not be judged under present circumstances.
Especially, F1 hybrids between wild species are population with high genetic and morphological uniformity and therefore, are less likely to include F1 hybrids exhibiting morphological forms (having the advantage of their both parents and far exceeding the traits of the both parents) desired by their breeder.
The genus Lobelia includes approximately 375 species with diverse properties such as annual, perennial, shrubby, woody properties, and most of them are native to tropical and warm-temperate regions.
Although there exist some interspecific cross combinations within the genus Lobelia that successfully produce hybrids (see Patent Documents 1 to 3), it has not been reported so far that reciprocal crossing between Lobelia richardsonii and Lobelia valida produces hybrids. All interspecific hybrids of Lobelia previously produced have been obtained only by traditional crossing. Thus, no report has described hybrids produced by the combination of cross and ovule culture.    [Patent Document 1]: U.S. Plant Pat. No. 10,758    [Patent Document 2]: U.S. Patent Publication No. 20020092044 A1    [Patent Document 3]: U.S. Plant Pat. No. 12,536
Lobelia valida (wild species) is tolerant of high temperatures and however, exhibits a poorly balanced and upright form. Moreover, it has a disadvantage of being less apt to become a large plant (plant bearing stems creeping sideways with thick, rising branching). Therefore, the breeding of Lobelia valida varieties that become large well-balanced plants has been desired.
On the other hand, Lobelia richardsonii (wild species) is tolerant of high temperatures and however, exhibits a fully trailing form. Besides, it has disadvantages of having very short flowering time because of its exceedingly strong long-day flowering habit and of less blooming. Therefore, the breeding of Lobelia richardsonii varieties that continually flower and profusely bloom has been demanded.
Thus, an object of the present invention is to find out a combination of two parents that gives F1 hybrids exhibiting an even distribution over a range from a hybrid close to the pollen parent to a hybrid close to the seed parent and possessing heat tolerance, and to breed a desired F1 hybrid therefrom.